Quenching and Irradiation Effects on Anion Ordering in (Tmtsf)2clo4

The anion ordering transition of (TMTSF)2ClO4, has been studied by X-ray diffraction down to 10 K. Influence of the cooling speed on the intensity and width of (0,1/2, 0) superstructure reflections is demonstrated. Partly quenched and relaxed states are characterized. X-ray irradiation has a very strong influence on the anion ordering. The transition temperature decreases and the reflection intensities are reduced upon irradiation. A preliminary analysis of 220 superstructure reflections shows that ordering of the anions accounts for most of their intensities so that associated lattice distortions are weak. This is in contrat with (TMTSF)2, ReO4, where the latter were important, especially for the organic stack.